The vast majority of hearing and balance impairments are thought to be due to death of sensory hair cells, the receptor cells of the inner ear. These cells are unusually metabolically active and hypersensitive to damage from overstimulation, exposure to some therapeutic drugs and environmental toxins, and to aging. However, there is enormous variability in structural and functional outcomes of these challenges to the inner ear among both humans and laboratory animals. The goals of our research program are to facilitate development of therapeutic agents to prevent hearing loss through understanding the cellular pathways and molecular identities of potential therapeutic targets that regulate death and survival of inner ear hair cells. During the proposed grant period we will: i) use the genetic potential and the accessibility of zebrafish lateral line neuromasts to better define cellular and molecular cascades that control hair cell death and survival following exposure to potentially ototoxic agents; ii) characterize drugs and small molecules that influence the susceptibility of hair cells when challenged by ototoxic agents; and iii) determine the efficacy of newly discovered genes and drugs in mammal inner ear and initiate preclinical development. Three groups of experiments are proposed: a) further examine intracellular calcium trafficking and ototoxin trafficking as determinants in the fate of ototoxin-exposed zebrafish and mammalian hair cells; b) determine intracellular pathways and mammalian efficacy of mutations in the Cc2d2a gene for hair cell protection in zebrafish and mammals; and c) further development of drugs and small molecule hits from completed screens toward preclinical efficacy for hearing protection.